1. Field of the Invention
The present invention relates to image display devices and particularly to solid state image display devices for providing two dimensional image displays in response to electrical signals applied thereto.
2. Prior Art
The present invention is a two-dimensional solid state display device which may be used for alpha-numeric displays or for the picture display in a television type device. Accordingly, the prior art relating to this type of display shall be discussed, though it is to be understood that the present invention has many other applications beyond those specifically mentioned therein.
There are three general types of display devices which are often considered, two of which have found widespread application. The first type of display device is a device having a limited number of areas of predetermined geometry and arrangement which may be caused to effectively create a light pattern, either by effecting light transmission (liquid crystal devices) or more commonly by emitting light due to some phenomenon (light emitting diode display devices etc.). Most of this type of display is used for the display of numeric information, and the display consists of either ten signal inputs, any one of which will cause the display of the numeral zero through nine, or will consist of seven segment arrangement in a block-eight form so that activation of various combinations of the seven segments will display the numerals zero through nine as desired. This type of display, utilizing various phenomenon, is fairly well developed and many types of devices are readily commercially available at a reasonable cost. The display, however, is extremely limited in the type and amount of information which may be displayed, and is typically limited to numbers of a fixed size such as may be used, by way of example, on digital read-out test equipment.
The second type of display device is a cathode ray tube, which is the only type of general capability two-dimensional display device which has found widespread application. This type of device may be used to display such things as alphanumeric information, time varying signals and pictures by the controlled deflection of an electron beam impinging upon a surface which will emit light in response to the electron beam, (or by the controlling of the electron beam deflection together with the intensity of the beam as in picture tubes for television sets). The cathode ray tube has the advantages that it may be produced for a reasonable price, electronically has a short time response, may be used to provide colors, and provides an image of good detail of any reasonable size required. It has the disadvantages, however, characteristic of a vacuum tube devices, that is, it requires a heated cathode and requires a high voltage source, not merely a few hundred volts, but on the order of 10,000 to 30,000 volts, and utilizes a rather large glass envelope.
The third type of display not yet finding commercial application is a solid state area display which would compete with the cathode ray tube in at least some applications. Many possibilities exist for such displays such as by way of example, a large array of light emitting diodes, each separately controlled so as to provide the image of the required resolution. Two problems exist with this type of display. First, the cost of such a light emitting diode array at the present time and even accounting for reasonable improvements in the state of the art, would be prohibitive. Secondly, the interconnection and addressing requirements, and, the support circuitry for the array, would be extremely complex and expensive. The technique, however, would have the advantage that each element in the array could theorectically be activated essentially continuously so that the present state of the art in emission intensity from such a device would probably be adequate.
Other techniques have been suggested, such as by way of example, the utilization of an array of some type of luminescent device arranged in rows and columns, with each location in the array being addressable to the respective row and column address line for that point in the array. While this type of system is consistent with the addressing techniques used in solid state random access memories and requires little support circuitry, it has the inherent disadvantage that each point in the array is activated a small portion of the time, so that the instantaneous brightness capability of the emitting device must be very high, typically greatly exceeding the present state of the art.
There is therefore a need for a simple solid state image display device which may be used to display two-dimensional images and which requires a minimum of support circuitry to provide a high quality two-dimensional image in response to electrical signal inputs at a reasonable total system cost.